Recent years have seen a rapid growth in interest in and commercial applications of ink jet printing technology. Many commercial systems today embody ink jets of the type disclosed in U.S. Pat. No. 3,298,030 issued to Lewis and Brown and U.S. Pat. No. 3,596,275 issued to Sweet, in which ink under substantial pressure is delivered to the ink jets, which produce a continuous stream of tiny droplets used for printing. U.S. Pat. No. 3,683,212 issued to Zoltan discloses an improved type of ink jet technology in which ink at atmospheric pressure or below flows to the jet by capillary action, where individual droplets are ejected on demand, rather than continuously.
In the drop-on-demand ink jet technology, the small size of the ink jet outlet, typically in the range of 0.00762 cm to 0.01279 cm, causes the system to be sensitive to particulates in the ink which could cause clogging of the outlet orifice. Such particulates may be due to dust and the like or precipitates in the ink itself. Also, the presence of minute air bubbles in the jet can lead to improper operation and loss of prime of the jet. In some instances, where the ink supply is located somewhat above the jet outlets, a sufficient pressure head may develop to cause dripping of ink from the jet.